Process for dyeing textile fibers with vat dyes



N. R. VIEIRA Filed March 11, 1944 PROCESS FOR DYEING TEXTILE FIBERS WITHVAT DYES Iruwl Feb. 4, 1947.

0 INVENToR.

ATTORNEY oa m' Wegma Patented feb. 4, 1947 1 PROCESS FOR DYEING TEXTILEFIBERS WITH VAT DYES Nicholas B.. Vieira, Charlotte, N. C., asslgnor toE. I. du Pont de Nemours & Company, Wilmington, Del., a corporation ofDelaware Application March 11, 1944, Serial No. 526,069

(ci. ss-149.3)

3 Claims. l

'I'his invention relates to an improvement in the process for dyeingtextile fabrics with vat colors, and, more particularly, to a processwhereby piece goods may be dyed in a continuous manner by a pigment paddyeing method.

There Vare two general methods in practice today for dyeing piece goodswith vat dyes. The first process, and the only one which has beenadapted for the continuous dyeing of piece goods as distinguished frombatch processes, is the one in which the vat color is applied to thegoods in the reduced form. Such processes are illustrated in the patentto Tice, U. S. P. 1,652,649, and the more recently developed process ofWentz U. S. P. 2,318,133. The dyeing of the ber from solutions of thereduced color presents some difficulties, however. In the rst place, theamount of dye that can be applied to the ber will depend upon howsoluble the color is in the reduced form, and the afiinity oi the dyefor the ber. Many of the anthraquinone vat colors are not readilysoluble in the vat, and therefore it is ditlicult to' apply them in theheavy shades required, without running the goods through the dye'bath asecond or third time. It has also been found difficult to dye cottongoods evenly in very weak or pastel shades by the reducedpad method,because of the tendency of thecolor to migrate on the goods in thepresence of the comparatively large amount of liquid that is taken up bythe goods in the dyeingy operation. It has also been found that, whendyeing in heavier shades with those vat dyes that are suillcientlysoluble to be applied in heavy shades, it is difncult in many cases toobtain the desired penetration. The reduced vat dyeing processes alsorequire large volumes of liquid from which the dye must be applied, foreven with the more soluble types they have limited solubility even inreduced form.

The second method generally employed in the dyeing of piece goods inwhat is commonly referred to as the pigment-pad reduction dyeingprocess, or the pad-jig process. VIn this process, the dye in a highlydispersed (unreduced) form is applied to the ber from concentratedsuspensions, and this finely suspended dye is forced into the fabric asthe cloth passes between squeeze rolls. The cloth is then run into rollseither without or after drying. These rolls are then put in a iig, inwhich the goods is rumback and forth several times through an alkalinereducing solution until the reduction and iixation of the dye on the beris complete. The goods is then run through an oxidizing bath orotherwise oxidized, then rinsed, soaped, re-rinsed and dried in thecustomary manner. This pad-jig process permits the application of thedye in as heavy strengths as desired, and the amount of water employedcan be reduced to only that'required to carry the suspended color intothe iiber under pressure of the squeeze rolls. This process, however,requires a large amount of handling of the goods and an unnecessarylength of time in passing the goods back and forth through the reducingsolution on the jig. Furthermore, because the fabric containing thereduced solution of the dye comes in contact with air, there is somesurface oxidation which is objectionable.

It is therefore an object of this invention to provide a process forapplying vat dyes to textile fibers by a pigment-pad process wherein thegoods can be continuously padded and developed without, extra handlingand without any chance of surface oxidation of the color on the fiberprior to complete development of the color thereon. A still furtherobject is to provide a continuous piece goods dyeing process which willgive results equally goodor better than those obtained by the knownreduced dyeing processes, particularly as to penetration and scrubfastness, and at the same time will obviate the handling of goodsrequired in the usual pad-jig method, and thereby speed up production.

It is a still further object of this invention to provide a continuouspiece goods dyeing process which will require the minimum volumes of dyeand chemical solutions, whereby greater output per unit may be attained,and wherein the bleedoff in the developing solution may be held to aminimum. It is a further object to provide aA process for dyeing piecegoods in a continuous manner which can be employed in applying colors inheavy shades in a single operation, such dyeing being equal in value tothose produced in the normal pad-jig method.

I have found that -textile iibers may be dyed with vat dyes by acontinuous dyeing process by padding -the vat color on to the cloth inpigment form, suchas in the usual pigment-pad method, then passing thecloth padded with the color through a reducing solution at a.temperature below that at which actual reduction of the dye takes place,and then immediately passing the goods into an air-free developmentchamber wherein the goods is alternately subjected to the action ofsteam and an alkaline reducing solution held at boiling temperature. Bythis process, reduction and xation of the color on the iiber takes placerapidly, and, because the amount of developing solution, namely, enemunio hydrosulte. in the developing chamber is kept at a minimum,equilibrium between the amount of color bleeding-oi! of the goods intothat solution, as more particularly disclosed and considered in Wentz U.S. P. 2,318,133 above-mentioned, is reached quickly.

By permitting-the greatest amount, of the development tobe carried outin the steam chamber above the developing bath and in the absence ofair, the amount of chemicals that must be continually added to thedeveloping solution is held usual manner with the pigment dispersion ofthe l4 tained at betwecnoit and 100%, hased'on the held and in which thegoods 2 is padded in the desired dye. It is then passed through squeezerolls l, by which the amount oi moisture and color to be retained in thegoods is controlled. The goods is then preferably passed through a hotnue l, whereby it may be dried by the means of air or other gases. Thedry goods, impregnated with the dye, is then passed through the chemicalpad I containing the caustic alkali and hydrosulte or other reducingagent, and through squeeze rolls I, whereby the amount of liquid to beretained in the goods can be controlled, after which it passes betweenguide rolls l into the developing chamber l, over and under rolls 9 andI 0,respectively, and then out of the developing chamber. After leavingthe developing chamber, .the goods containing the dye developed thereinis passed through squeeze rolls Ii and then subjected to the usualoxidizing, rinsing, soaping,

rinsing, and drying processes, all of which can be carried out in thecontinuous piece in the same manner as in the reduced-pad continuousdyeing processes.

For convenience, the developing'chamber I is divided into sections bypartitions I5 and I E, so that it is possible to employ solution in onlyone or two of the sections, depending upon the amount of time that theparticular ber impregnated with dye and reducing agent is to besubiected to the steam atmosphere, and for how long or how often it isto be immersed in the alkali developing solution to obtain'thedeslred'result. Steam may be introduced through inlets i'l or il, orboth, to maintain the solution and atmosphere at the desiredtemperature.

Although, as indicated in the drawing, the goods after being padded withthe dye is preferably passed through a hot flue or over otherdryingapparatus before it is impregnated with the chemical pad. this is not anessential requirement in the process. If the chemical pad is applied tothe wet pigmented goods, the moisture content of the ilnal l chemicalpadded goods should not be over 100%, based on the weight of the drygoods. Control of this moisture content of the impregnated fabric priortoits passage into the developing chamber has been found desirable inthe production of level dyeings, foi excessive moisture will tend tocause streaking. With most dyes and with most fabrics, satisfactoryresults are obtained with the moisture content of the weight of thefabric.

As illustrated in the diagrammatic sketch, suitable means are providedfor introducing the developing solution into the various compartmentsand for maintaining any predetermined level of the solution in thecompartment.

By passing the goods directly from the reducing pad into the developingchamber, from which al1 air or oxygen is excluded, thev reduction andfixation of the color is rapidly effected. Where maximum penetration,or, in other words, minimum migration of the dye to the surface, isdesired. the number of dips oi' the cloth into the developing solutionin the developing chamber is reduced to a minimum. In certain cases,however, it is desired to increase the apparent strength of the dye onthe goods by causing some small amount of migration of the dye tothesurface of the ber. By the process of this invention, wherein .thedevelopment is carried out partly in the steam above the developingbath, the

amount of migration can be carefully controlledV solution in thedeveloping chamber, as more particularly described in the development ofreduced-pad dyeings in the Tice and the Wentz patents above-mentioned.However, if no dye is added an equilibrium is soon reached, and thedyeing then remains at a constant shade.

The ldevelopment of the vat dye on the lliber at temperatures of 212 F.or somewhat higher has been found to very greatly increase 'the speed atwhich the dyeing can be effected. and also has been found to improve thequality of the resulting dyeings with regard to penetration andresulting fastness, particularlyas to Y laundering and scrubbing.-

To prevent premature reduction of the dye on the liber after passing itthrough the chemicalpadding solution, the chemical-padding operation,namely, the application of the alkaline reducing solution, should becarried out at temperatur'es preferably not over 90 F. Temperatures ashigh'as 110 F. may be employed, provided the time of immersion in thechemical solution is held at a minimum and the goods is vpassedimmediately into the developing chamber.

ical pad should be from 2 to 10 seconds, although a longer time may berequired for certain types4 of fabrics. The timel of immersion should bekept at the minimum required to obtain complete penetration of thechemical solution to the goods.

Following the chemical-padding operation, it is desirable that `thegoods be passed as directly and quickly as possible into the developingchamber to avoid any tendency toward decomposigoods. as it enters thedeveloping chamber, main'- -'ns tion of the 'reducing agent, oroxidation of any reduced dye. Experience has shown that no appreciabledecomposition can be detected when y chamber.

The temperature in the developing chamber is held at, or slightly above,the boiling point of the developing bath. While higher temperatures maybe employed, their use requires the use of increased pressure in thedeveloping chamber so that the developing solution will not bevaporized. With increased temperatures above the boiling point of theliquid, a reduction in the time required to effect complete developmentcan be attained. At temperatures of 212 F., or slightly above,substantially complete reduction and iixation of the dye is obtained infrom 30 to 60 seconds. Longer periods in the developing bath may berequired with certain types of ber. After development and xation in thedeveloping chamber, the cloth is run into the usual oxidizing baths.Chromic acid, sodium perborate, hydrogen peroxide, or other oxidizingagent Vmay be employed, or the dye may be oxidized on the goods by meansof air. After oxidation, the' goods is soaped, rinsed and dried in theusual manner.

To facilitate the chemical-padding operation, wetting agents may beemployed Alkanol B (sodium alkyl-naphthalene sulfonate) operates veryeffectively for this purpose when added to the pigmented-pad bath.

The following examples are given to illustrate the invention. Unlessotherwise speciiied, the parts used are by weight.

Example 1 A mixture containing 0.25 oz. per gallon of the dyestui ofExample 1 of U. S. P. 2,212,029, 0.37

oz. per gallon of pentanthrimide carbazole (U .S. P. 2,028,103), and0.44 oz. per gallon of the dyestuff of U. S. P. 1,525,117 is padded onherringbone twill with the padder set for moisture retention, and theimpregnated goods then dried.

The impregnated fabric is then padded a second time with 50% moistureretention with a solution consisting of 1.5 oz. per gallon of causticsoda and 4 oziper gallon of sodium hydrosulflte at a temperature of 70F. The fabric is then passed through the developing chamber, asillustrated in the accompanying drawing, where the developing solutionis present in all three of the compartments, at such a rate that it issubjected to the action of the steam and the developing solutioncontaining 1.5 ozs. per gallon of caustic soda and 1.5 ozs. per gallonof sodium hydrosulte, for a. period of one minute. The amount ofsolution maintained in the bottom of the developing chamber is suchthat, for one-fth of the total time the cloth is in the developingchamber, it is passing through the developing solution. The liquid inthe booster is under a head of steam at 212 F. The impregnated cloth isthen oxidized in the conventional manner in a 0.25% chromo-acetic acidsolution, rinsed, soaped, rinsed and dried. The fabric is dyed an olivedrab shade with good penetration and fastness to laundering andabrasion.

Example 2 The fabric is padded with a dyestuil suspension and in thechemical pad, as in the preceding example, and then passed in one minutethrough a three-section booster, as' illustrated in the drawing, ofwhich only the third section contains caustic soda and hydrosulte in thesame ratios as in the preceding example, so that, while in thedeveloping chamber, the goods is immersed in the developing solution foronly onefteenth ofthe time. The goods is oxidized in the conventionalmanner. The dyeing is apparently somewhat weaker (5%) than that of thepreceding example, but the penetration and the fastness to launderingand abrasion are somewhat better.

Ezvample 3 The fabric is padded with a dyestufi suspension and thereducing solution as in Example 1, and then passed in one minute througha threesection booster, as in Example 2, where only the third sectioncontains 1.5 oz. per gallon caustic soda, 1.5 oz. per gallon of sodiumhydrosuliite and 0.10 oz. per gallon of the dyestuff mixture in theproportions given in Example 1. The impregnated cloth is then oxidizedin the conventional manner in a 0.25 chrome acetic acid solution,rinsed, soaped, rinsed and dried. The fabric is an olive drab shadeapproximately 5% to 10% stronger than that obtained by the process ofExample 1. Penetration was excellent, and the fastness to laundering andabrasion was fully equal to that of Example 2.

Example 4 A mixture containing 0.621 oz. per gallon o! pentanthrimidecarbazole, 0.587 oz. per gallon of the dyestuif of Example 1 of U. S. P.2,212,029, 0.104 oz. per gallon of the dyestuff of Color Index #1150,0.104 oz. per gallon'of the dyestuil of Color Index #1151, and 0.400 oz.per gallon of Alkanol B (sodium alkyl naphthalene sulfonate) is paddedon herringbone twill with the pad set for 50% moisture retention, andthe impregnated goods then dried.

The impregnated fabric is then padded a sec` ond time with 50% moistureretention with a solution consisting of 6 oz.per gallon of caustic soda,6 oz. per gallon of sodium hydrosulte and 6 oz. per gallon of commonsalt, at a temperature of F. The fabric is then passed in one minutethrough a steam development chamber containing a three-section booster,as in Example 2, where only the third section contains 1.5 oz. pergallon of soda ash, 0.05 oz. per gallon of caustic soda, 0.40 oz. pergallon of sodium hydrosulte, and 4 oz. per gallon of common salt at 212F. Sections one and two contain only steam. The

.impregnated cloth is then oxidized in the conventional manner in a0.25% chrome acetic acid solution, rinsed, soaped, rinsed, and dried.The fabric is an olive-drab shade approximately 10% stronger than thejig development. Fastness to rubbing and laundering is noticeablysuperior to both the jig and reduced pad-continuous processes. Thepenetration is equal to the jig process but noticeably superior to thereduced padcontinuous processes.

Additions of 0.1% to 10% of the concentration of color in thepigment-pad may be added to the `booster bath to obtain additionalstrength in the dyeing.

As illustrated in the above examples, the amount of time in which thegoods is developed in the steam and in the developing solution can bevaried by employing developing solution in only one or more of thecompartments, as well andere" r tion through which the goods musttravel. with certain types of ber. it has been found desirable that 'thegoods while in the developing cham-- ber should be subjected severaltimes to the developing solution, while withother types of goods anddyes only one pass into the developing solution may be required toproduce the desired result It is preferabley that the cloth on enteringthe developing chamber be heated quickly to the temperature of thechamber, and the heating should be carried out in such a manner that itis uniform on both sides of the fabric. The flow of steam through theapparatus should be regulated in such a manner 'that the decompositionproducts of the reducing agent. etc., are continu ally removed. Theformation or deposition of moisture as condensate on the fabric shouldbe avoided.

'Ihe processA of this invention may be employed in the dyeing not onlyof cellulosic materials, but in' the dyeing of other bers and mixedfabrics, for example, those containing or consisting of nylon.viscose-cotton mixtures, acetate-rayonviscose mixtures, etc. It isofcourse imderstood thatv other vat dyes than those specifically emlployed above may be dyed by this method, such as the thio-indigos,sulfur colors, etc., which are dyed by the vat dyeing method.`

In place of sodium hydrosulte. other reduc- .ing agents which operate ina similar manner may be employed. 'Ihe time required for completereduction and development in the developing chamber will depend upon theease with which the particular color is reduced and upon the type of berbeing dyed. The process is particularly suitable for dyeing very tightlywoven fabrics, such as Indian Head fabric, in even shades.- This typeofgoods is diiilcult to dye in even shades by the ordinary reduced-paddyeing methods.

This process provides a satisfactory method for dyeing goods in thecontinuous piece. where the dye is applied by pigment-pad process.Because the development is carried out partly in steam and with only asmall volume of developingsolution, the amount of chemicals and dyerequired in Vthe developing bath is reduced to a minimum. The processpermits the dyeing in a continuous manner by pigment-pad method, wherebyheavy shades can be obtained with dyes that will not produce heavydyeings by the usual reduced-pad dyeing methods. The dyeings ex hibitexcellent penetration and have fastness properties approximating thefastness of the dyeings obtained by the usual pad-jig dyeing method.They exhibit substantially better fastness to rubbing and launderingthan the dyeings obtained by the continuous reduced-pad dyeing method.

The process of this invention is applicable for the dyeing of warps,skeins, or any other form of o s pigment pad,'chemical pad-anddevelopment chamber in 'a continuous manner.-

Otherndvantages of the pigment-pad dyeing processes heretofore operatedare obtained in dyeing piece goods in the continuous manner, asdistinguished from thepad-iig methods hereto fore required.

I claim:

1. In a continuous process for dyeing textile fibers with vat dyes.' thesteps which comprise padding the fiber, which has been impregnated withunreduced dye inf pigment form, with a caustic alkali solution of areducing agent under conditions which do not immediately reduce the vatcolor on the ber, and then alternately subjecting the ber padded withcolor andhreducln! agent to the action of steam and an alkali solutionofareducing -agent to-enect development of the color on the ber, saiddevelopment treatment being continued until substantially all ofthecolor has been reduced and ilxed in the ber, said treatment in alkalinereducing agent and steam being carried out in the absence of air.

2. In a continuous processfor dyeing textile fibers with vat dyes, thesteps which comprise padding the ber, which has b een impregnated withunreduced dye in pigment form, with -a caustic alkali solution of areducing agent under conditions which do not immediately reduce the vatcolor on the ber, and immediately subjecting the ber padded with colorand reducing agent to the action of steam and then alternately textileber which can be introduced into the' Q A l to the action of steam andan alkaline solution of reducing agent to effect development of thecolor on. the ben said development treatment being continued untilsubstantially all of the color has been reduced and xed in the ber, saidtreatment in alkaline reducing agent and steam being carried out in theabsence of air.

3. The'process of claim 1, inwhich some of the color originally employedin the padding of the ber is added to the development solution toprevent initial bleeding-oil of the color in the ber into the developingbath.

Y I NICHOLAS R. VIEIRA.

REFERENCES CITED The following *references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 2,164,930 Lubs July 4, 19392,151,363 Wedler Mar. 21, 1939 2,204,839 Wedler June 18, 1940 1,663,845Jacoby Mar. 27, i928 1,979,818 Baker Nov. 6, 1934 2,071,922 Drobile Feb.23, i937 1,868,300 Wylam July 19, 1932 1,019,092 Schwarz Mar. 5, 19121,832,425 Remlein Nov. I7, 1931 521,816 Rmtt June 26, 1894 '161,107Rovira May 31, 1904

